This invention relates to an automatic recording fluorometer/densitometer, and more particularly to an automatic valley sensor for such an instrument.
A recording fluorometer/densitometer is used to analyze the electrophoretic characteristics of a clinical sample.
U.S. Pat. Nos. 3,479,265 and 3,635,808 disclose thin film agarose sample plates which can be used as the electrophoretic medium. The thin film samples of these patents are particularly convenient for handling and storage.
These samples are analyzed by fluorometric or densitometric optical detection. One instrument for automatically making analyses of this type is described in U.S. Pat. No. 3,706,877. In such an instrument, the area under selected peaks of the curve is determined by integration. In order to perform the integration under selected peaks it is necessary to select the valleys between peaks so that the valleys can be used to define the limits of integration.
Automatic valley selection can be based upon the discrimination of certain characteristics of slope and curvature extant at desired valley points. Slope and curvature information can be derived from the first and higher derivatives of the signal. A problem with current use of derivative information is that the magnitude of electronic time-delay effects, the magnitude of sample-derived noise, and the values of curvature and slope near the extrema of a multicomponent profile are largely proportional to the magnitude of the components; hence, fixed values of slope and curvature cannot be used as reliable, shape-sensitive criteria for valley selection if the component peaks are not relatively uniform in size. For example, electrophoresis profiles are often composed of a number of peaks that are rather similar in shape, but quite different in amplitude. This makes it impossible to select shape equivalent integration limits for the peaks on the basis of fixed values for the first and higher derivatives, because all of these derivatives are proportional to the scale height of the peaks.